This invention relates to a refrigerant circuit, in an ice making machine and the like in which ice pieces formed on ice making plates and the like are released therefrom by allowing a high-temperature and high-pressure vaporized refrigerant from a compressor to flow into an evaporator, which enables secured and stable releasing of the ice pieces even when the ambient temperature is low.
An ice making machine for making automatically a number of ice pieces has a freezing circuit for circulating a refrigerant, in which the ice making plates are designed to be heated by feeding a high-pressure and high-temperature vaporized refrigerant (hereinafter sometimes referred to as hot gas) from a compressor to the evaporator attached to the ice making plates, upon switching from a freezing operation to an ice releasing operation, to accelerate releasing of the ice pieces formed on the ice making plates. For example, FIG. 11 shows a flow-down system ice making machine, in which water to be frozen is sprinkled against ice making plates standing perpendicularly to form ice pieces continuously thereon. In this type of ice making machine, an evaporator 14 led out of a freezing circuit 12, shown in FIG. 12, running zigzag in the transverse direction is secured in closed contact between a couple of ice making plates 10 disposed perpendicularly, and a refrigerant is circulated through the evaporator 14 during the freezing operation to forcibly cool these ice making plates 10. A plurality of vertical elongated ridges 10a are arranged on the freezing surface of each ice making plate 10 in the transversal direction, and ice pieces 16 are designed to be formed between every two adjacent ridges 10a at the positions where the evaporator 14 runs. A slanted water collecting plate 18 having a plurality of through holes 18a is disposed immediately below the ice making plates 10, and the portion of the water to be frozen which was fed to the ice making plates 10 during the freezing operation but failed to freeze is dripped through the through holes 18a to be recovered and stored in a water tank 20 locating below the water collecting plate 18. Incidentally, the water collecting plate 18 also serves to guide the ice pieces 16 released from the ice making plates 10 under the ice releasing operation and dropped to the plate 18 into an ice bin 22 disposed diagonally below the water collecting plate 18.
A water supply pipe 26 led out of the water tank 20 through a circulating pump 54 is connected to a sprinkler 28 disposed above the ice making plates 10 and on the freezing surface sides thereof. A plurality of water distribution holes (not shown) are formed in this sprinkler 28, and the water to be frozen pumped up from the tank 20 during the freezing operation is designed to be sprinkled through these water distribution holes onto the freezing surfaces of the ice making plates 10 cooled to the freezing point and to flow down therealong, whereby to form ice pieces 16 having a predetermined shape on the freezing surfaces.
FIG. 12 shows schematically a constitution of the freezing circuit to be suitably employed in the above-described automatic ice making machine. The freezing circuit 12 essentially has a compressor 30 for compressing a refrigerant such as Freon, a condenser 32 to which the high-pressure and high-temperature vaporized refrigerant obtained after compression in the compressor 30 is fed, an expansion valve 34 to which the refrigerant condensed to be liquefied in the condenser 32 is fed and an evaporator 14 to which the refrigerant expanded to be vaporized through the expansion valve 34 is fed. The evaporator 14 performs heat exchange with the refrigerant expanded and vaporized through the expansion valve 34 so as to cool the ice making plates 10 attached to the evaporator 14 below the freezing point and allow the water to be frozen flowing down along the ice making plates 10 to freeze gradually. The vaporized refrigerant heated after heat exchange in the evaporator 14 is fed back to the compressor 30, compressed to a high pressure and a high temperature and then recirculated. Incidentally, the reference number 36 denotes a detecting means for detecting the temperature of the refrigerant on the refrigerant outlet side of the evaporator 14, and the detecting means 36 is designed to perform aperture control of the expansion valve 34.
A pipe 38 branching out of a pipe 37 locating on the outlet side of the compressor 30 is connected via a hot gas valve 40 such as a solenoid valve to the inlet side of the evaporator 14 to constitute a so-called hot gas circuit 42. The hot gas valve 40 is closed during the freezing operation to interrupt circulation of the refrigerant through the hot gas circuit 42 and to circulate the refrigerant to the freezing circuit 12 only. Meanwhile, when the ice releasing operation for releasing and dropping the ice pieces is started after completion of the freezing operation at the ice making plates 10, the hot gas valve 40 is let open to allow a hot refrigerant (hot gas) to circulate through the hot gas circuit 42. Thus, the ice making plates 10 attached to the evaporator 14 are heated to release adhesion of the ice pieces 16 formed on these ice making plates 10 and allows them to drop by their own weights.
As described above, when the operation mode of the ice making machine is switched to the ice releasing operation, the hot gas valve 40 is changed over from the closed posture to the open posture (1) to interrupt circulation of the refrigerant through the freezing circuit 12 and (2) to feed the high-pressure and high-temperature vaporized refrigerant from the outlet side of the compressor 30 to the evaporator 14. However, as shown in FIG. 12, no closing means such as a valve is disposed on the inlet side of the condenser 32. Accordingly, the hot gas delivered from the compressor 30 during the ice releasing operation is not entirely fed to the hot gas circuit 42, but the substantial portion of the hot gas is designed to be circulated through the hot gas circuit 42. The small portion of the hot gas flows into the condenser 32 where the heat is dissipated well, and the hot gas is liquefied and stays therein (this phenomenon is termed as "stagnation"). If some portion of the hot gas stagnates in the freezing circuit 12 connected to the condenser 32, the hot gas to be circulated through the hot gas circuit 42 decreases with time corresponding to the amount of stagnation. It can thus be pointed out that the ice releasing performance in the evaporator 14 is gradually lowered to require a considerable time for the ice releasing operation, disadvantageously. Such problem occurs conspicuously, particularly when the ambient temperature is low. Incidentally, in the freezing circuit of a system in which a receiver is provided on the outlet side of the condenser 32, the amount of stagnated hot gas is increased, so that the ice releasing performance is further lowered.
A countermeasure for such problem is proposed, in which a solenoid valve 44 is disposed, as shown in FIG. 13, on the downstream side (on the condenser (32) side), with respect to the flow of the refrigerant, than the junction of the pipe 38 with the pipe 37 connecting the compressor 30 to the condenser 32. Namely, during the freezing operation, the solenoid valve 44 is let open to allow the refrigerant to circulate through the freezing circuit 12, and also the hot gas valve 40 is closed to interrupt circulation of the refrigerant through the hot gas circuit 42. Meanwhile, when the operation mode is switched from the freezing operation to the ice releasing operation, the solenoid valve 44 is closed to interrupt circulation of the refrigerant through the freezing circuit 12, and also the hot gas valve 40 is let open to allow the heated refrigerant (hot gas) to circulate through the hot gas circuit 42. Thus, the hot gas delivered from the compressor 30 during the ice releasing operation is entirely fed to the hot gas circuit 42 so as to prevent drop in the ice releasing performance, enabling reduction of the time required for the ice releasing operation.
It should be noted here that when the ambient temperature is low like in winter, the ice releasing performance frequently becomes insufficient, as described above, but when the ambient temperature is high like in summer, very high ice releasing performance is not required. Accordingly, if the solenoid valve 44 is closed regardless of the ambient temperature, when the operation mode is switched from the freezing operation to the ice releasing operation, a large amount of hot gas flows through the hot gas circuit 42 particularly under the condition where the ambient temperature is high (high temperature, e.g. 20.degree. C. or higher). Then, the ice making plates 10 are heated very much to increase the recycling freezing time or to excessively increase the pressure on the refrigerant inlet side of the compressor 30 (lower level pressure) and apply a great load to the compressor 30, leading to liability to drop in the ice making performance or breakdown of the compressor 30.
In the ice making-machine described above, a thermostat is disposed correspondingly on the outlet side of the evaporator 14 provided between the ice making plates 10, so that the temperature rise in the evaporator 14 due to the increased amount of the hot gas flowing without undergoing heat exchange after releasing of the ice pieces 16 from the ice making plates 10 may be detected by the thermostat to complete the ice releasing operation. In this case, in the state where the solenoid valve 44 is let open so as to start the ice releasing operation and the hot gas is entirely circulated through the evaporator 14 even if almost all of the ice pieces 16 are released from the ice making plates 10 to apply reduced load thereto near the end of the ice releasing operation, substantially the same amount of hot gas is circulated as in the case where a great load is applied to the ice making plates, so that the temperature of the evaporator 14 is occasionally elevated speedily to allow the thermostat to detect completion of the ice releasing. In other words, although some ice pieces 16 still remain on the ice making plate 10, the freezing operation is resumed, leading to double-freezing, disadvantageously. Such trouble occurs particularly when the ambient temperature is extremely low (very low temperature, e.g. 0.degree. C. or lower).